there is a possibility that your shift linkage is messed up. if not that then it is a sensor.
loose wire or most likely ignition module
The 2006 Jeep Grand-Cherokee has rear wheel drive.
The 2003 Jeep Grand-Cherokee has rear wheel drive.
The 2011 Jeep Grand-Cherokee has rear wheel drive.
The 2005 Jeep Grand-Cherokee has rear wheel drive.
The 2007 Jeep Grand-Cherokee has rear wheel drive.
The 2004 Jeep Grand-Cherokee has rear wheel drive.
The 2008 Jeep Grand-Cherokee has rear wheel drive.
The 2009 Jeep Grand-Cherokee has rear wheel drive.
The 2013 Jeep Grand-Cherokee has rear wheel drive.
The 2014 Jeep Grand-Cherokee has rear wheel drive.
A Grand Cherokee is either rear wheel drive or four wheel/all wheel drive.